1. Field of the Invention
The present invention relates to a process for the preparation of bumps on integrated circuits (ICs). The object is to avoid an (expensive) sputtering process required for the preparation of prior art bumps.
2. Prior Art
The flip-chip--or Tape Automated Bonding (TAB)--technology is a bonding process interconnecting the chip via "bumps" with a printed or prepared circuit structure on (semiconductor-) substrates. These processes allow high connection rates on a very small surface, lower inductivities as compared with wire bondings and an improved transfer of heat or thermal conveyance. At present, solder bumps or gold bumps are commonly used in said flip-chip and TAB technology. These processes require entire wafers as well as the use of thin-film-technologies (sputtering, photoresist-structuring) in combination with galvanic metal deposition processes.
Wafers comprising aluminum bond pads and a passivation layer are used for the galvanic shaping or molding of bumps in photosensitive resist. The passivation layer covers the entire wafer--thus sufficiently protecting the active elements--only the aluminum bond pads are left open and are overlapped on the edges by the passivation. The bumps may not be deposited directly on said aluminum pads, because metallic interconnections are formed at the surfaces adjoining the aluminum. Therefore, an adhesion and diffusion barrier layer (e. g. TiW) is prepared by sputtering after a preceding sputtering and etching process. A second thin gold or copper layer is sputtered, to form a basis for the gold or solder bumps to be deposited by galvanization. Said layer system is also called "under-bump-metallization". A galvanic mask consisting of photosensitive resist is required for the preparation of the bumps. In order to obtain a high contact density, the horizontal growth may be limited by using a thick photosensitive resist. The galvanic shaping of the bumps is effected in a respective metal bath.